fix recipes order with hostpython/python alias that didnt work in the first run

recipes/hostpython.py

@@ -7,9 +7,15 @@ class HostpythonAliasRecipe(Recipe):
     def init_after_import(self, ctx):
         hostpython = ctx.state.get("hostpython")
         if not hostpython:
-            print("WARNING: no hostpython set yet, so you need to specify")
-            print("WARNING: either hostpython2 or hostpython3 in your deps")
-        else:
+            # search in wanted_recipes if it's the first time
+            if "hostpython2" in ctx.wanted_recipes:
+                hostpython = "hostpython2"
+            elif "hostpython3" in ctx.wanted_recipes:
+                hostpython = "hostpython3"
+            else:
+                print("WARNING: no hostpython set yet, so you need to specify")
+                print("WARNING: either hostpython2 or hostpython3 in your deps")
+        if python:
             self.depends = [hostpython]
 
 recipe = HostpythonAliasRecipe()

recipes/python.py

@@ -7,9 +7,15 @@ class PythonAliasRecipe(Recipe):
     def init_after_import(self, ctx):
         python = ctx.state.get("python")
         if not python:
-            print("WARNING: no python set yet, so you need to specify")
-            print("WARNING: either python2 or python3 in your deps")
-        else:
+            # search in wanted_recipes if it's the first time
+            if "python2" in ctx.wanted_recipes:
+                python = "python2"
+            elif "python3" in ctx.wanted_recipes:
+                python = "python3"
+            else:
+                print("WARNING: no python set yet, so you need to specify")
+                print("WARNING: either python2 or python3 in your deps")
+        if python:
             self.depends = [python]
 
 recipe = PythonAliasRecipe()

toolchain.py

@@ -1051,6 +1051,7 @@ def build_recipes(names, ctx):
     # gather all the dependencies
     print("Want to build {}".format(names))
     graph = Graph()
+    ctx.wanted_recipes = names[:]
     recipe_to_load = names
     recipe_loaded = []
     while names: